In the production of various chemical products, glutaraldehydes are important and useful as an intermediate starting material. Furthermore, they have many usages such as a tanning agent, a hardening agent for microcapsules, a germicide, a cross-linking agent, an enzyme fixer and the like.
Currently, glutaraldehydes are generally produced through a two-step reaction process which comprises a Diels-Alder reaction between acrolein and vinyl ether, and a hydrolysis of the resultant 2-alkoxy-dihydropyran. However, this process has drawbacks that the reaction time is too long, and that the starting materials are expensive and also are not easily available.
In addition to the above process, it is also well known to oxidize 1,5-pentanediols to produce the corresponding glutaraldehydes. However, this process suffers from the drawbacks such that the starting materials are expensive and the resulting glutaraldehydes have a very poor purity. Accordingly, the cost of the commercially available glutaraldehydes increases and is generally remarkably higher than that of other chemical products. It is therefore desirable to develop a production process of glutaraldehydes having a good purity from low-cost and easily, chemically synthesizable starting materials.
From these industrial viewpoints, it is expected to develop a production process of glutaraldehydes by using as a starting material cyclopentene or its derivatives which are industrially available at a relatively low cost. However, it has been already well-known that glutaraldehydes can be produced through oxidation of cyclopentene or its derivatives. Generally, this process comprises synthesizing 1,2-cyclopentane-diol from cyclopentene and then oxidizing the resulting 1,2-cyclopentane diol with an oxidizing agent such as lead tetraacetate or periodic acid. This process exhibits a good selectivity, but lead tetracetate and periodic acid used therein tend to be stoichiometrically consumed without additionally acting as a catalyst. Furthermore, it has been also well-known that cyclopentene is reacted with ozone to form the corresponding ozonide and the ozonide is then subjected to a reduction decomposition to produce glutaraldehydes. This process, however, is not suitable in an industrial production process of glutaraldehydes, since ozonide which is produced as an intermediate of the process has a risk of explosion.
Recently, a catalytic oxidation of cyclopentene or cyclopenteneoxide with hydrogen peroxide in the presence of molybdenum compounds is proposed in, for example, Japanese Patent Publication (Kokoku) Gazette Nos. 52-28606 and 51-33526. However, this catalytic oxidation process has important problems which must be solved.
A first problem of the catalytic oxidation process is that the reaction must be carried out in a non-aqueous system, since the reaction will be stopped if there is any water in the reaction system. This means that a commercially available aqueous solution of hydrogen peroxide at a low concentration is not suitable for use in this process and therefore it must be further extracted with an organic solvent to obtain water-free hydrogen peroxide. Further, in spite of use of water-free hydrogen peroxide, this process suffers from additional water problem. Namely, since water is produced during the reaction of cyclopentene or cyclopenteneoxide with hydrogen peroxide, it must be continuously removed from the reaction system.
A second problem of the process resides in that a plurality of 1,2-cyclopentanediols are produced as a by-product. It is therefore essential to reduce formation of such a by-product, since the by-product is difficult to separate from glutaraldehydes and therefore causes a reduction of the yield of the resulting glutaraldehydes.
A third problem of the process resides in that molybdenum compounds as the catalyst can be separated from the resulting glutaraldehydes with difficulty. This is because the molybdenum compounds are solubilized as a result of the reaction with hydrogen peroxide and an organic hydroperoxide. The solubilization of the molybdenum compounds is unavoidable, even if they are supported with a carrier material such as silica or alumina. Therefore, this process needs much effort for the purpose of recovering the catalyst.
The most important and fourth problem of the process resides in a further reaction of the resulting glutaraldehydes. Since glutaraldehydes are very unstable, they will be further oxidized to the corresponding carboxylic acids or they will be wastefully consumed in the accompanying condensation reaction, if the reaction is continued without separating the resulting glutaraldehydes from the reaction system.
Summarizing these problems, it is clear that the catalytic oxidation process described above does not ensure the production of glutaraldehydes having a high purity at an elevated yield. It is therefore considered that the production of glutaraldehydes in an industrial production scale can be attained with remarkable difficulty, when cyclopentene or cyclopenteneoxide is oxidized with hydrogen peroxide to produce glutaraldehydes.
In view of the above facts, it is generally concluded that, in the production of glutaraldehydes, their instability should be discussed in addition to ease of the practice of the process and yield of the resulting glutaraldehydes. For example, assuming that the proposed process for the production of glutaraldehydes can provide a higher yield, the process is considered to be insufficient for the industrial production purpose if it accompanies further reaction of the resulting glutaraldehydes and requires consumption of the energies for removing impurities.
Under these circumstances, we made efforts to find out a production process which enables effective production of glutaraldehydes which are important chemical starting materials, at a low cost, and completed the present invention which will be described hereinafter.